Objective: To assess whether reproductive factors are associated with mortality after breast cancer diagnosis.
Methods: We followed up 4,299 U.S. women enrolled between 1980 and 1982 at ages 20-54 years as incident breast cancer cases in a population-based, case-control study, the Cancer and Steroid Hormone Study. Vital status through 1997 for these cases was obtained by linking Cancer and Steroid Hormone Study data to Surveillance, Epidemiology, and End Results files. We estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for death associated with selected reproductive factors using proportional hazards models.
Results: During a median follow-up of 14.5 years, 1,847 deaths occurred. Women aged 20-45 years whose last birth occurred 12 months or less (age-adjusted HR = 1.62, 95% CI 1.10-2.37) and 13-48 months before breast cancer diagnosis (age-adjusted HR = 1.35, 95% CI 1.05-1.75) were at an increased risk for death compared with nulliparous women. After adjusting for additional factors including tumor stage, women whose last birth occurred 12 months or less before diagnosis remained at an increased risk for death (HR = 1.51, 95% CI 1.02-2.23). Fifteen-year survival was 38%, 51%, and 60% among women aged 20-45 years whose last birth was 12 months or less, 13-48 months, and more than 48 months before diagnosis, respectively, compared with 65% among nulliparous women. Mortality risk was not associated with age at first birth, parity, or breastfeeding duration among women aged 20-45 years or among women aged 46-54 years.
Conclusion: A recent birth may be an adverse prognostic indicator among women diagnosed with breast cancer at ages 20-45 years.